In an existing technique, an ultraviolet irradiator has been used for curing an ultraviolet-curing resin used as an adhesive around a flat panel display (FPD) or an ultraviolet-curing ink used as an ink for sheet-fed printing.
As the ultraviolet irradiator, a lamp-type irradiator using a high-pressure mercury lamp or a mercury xenon lamp as a light source is known in the art. Recently, an ultraviolet irradiator using a light emitting diode (LED) as a light source instead of an existing discharge lamp is being developed in order to reduce power consumption, extend a life span and allow a compact design (e.g., Patent Literature 1).
An ultraviolet irradiator disclosed in Patent Literature 1 includes a first light irradiating device disposed to face an ultraviolet-curing ink irradiated surface of an irradiation target, and a second light irradiating device disposed to face a non-irradiated surface positioned opposite to the irradiated surface. Here, an ultraviolet ray from the first light irradiating device and an ultraviolet ray from the second light irradiating device are simultaneously irradiated to the irradiation target to enhance adhesion between the irradiation target and the ultraviolet-curing ink.
In order to emit light from the LED, a voltage over an operation voltage VF should be applied and a predetermined current should flow. For this reason, in the ultraviolet irradiator using a LED as a light source, a so-called switching power supply device for converting AC power supplied from an AC power source AC (commercial power) into DC power is used (e.g., Patent Literature 2)